Aquarium heater

ABSTRACT

An aquarium heater including a housing and a tube depending therefrom. An electric heating element is disposed in the bottom portion of the tube and a thermostatic control chassis is disposed in the upper portion of the tube. The control chassis includes two opposing housing sections matingly engaged in a nesting relationship to form a cylindrical housing unit which snugly fits into the tube and supports a bimetallic thermostatic switch together with associated circuitry and lead wires such that the thermostatic circuit elements are maintained securely positioned within the tube. The housing includes a gasket situated between a lip of the tube and the bottom wall of the housing, and a locking ring which clamps the rim of the tube in place. The tube is thereby held securely to the housing independently of the control chassis. A vertically slidable actuator arm engages a circular cam surface in the housing, where the cam surface converts rotary motion of a knob into vertical motion to thereby move the actuating arm. The lower end of the actuating arm engages and positions an adjustable contact member of the thermostatic switch to thereby maintain the temperature level of the heater as close as possible to a desired value.

BACKGROUND OF THE INVENTION

This invention relates to an aquarium heater and more particularly to aheater which can maintain its operation in a more accurate, efficient,and safe manner.

Aquarium heaters are generally utilized for maintaining a desiredtemperature level in aquarium tanks in order to provide a suitableenvironment for sustaining and propagating the fish contained in thetank. As a result, it is necessary to provide the heater withappropriate thermostatic means in order to sense the changingtemperature in the tank and to thereby appropriately turn on and off theheater to maintain the temperature level as close as possible to thedesired value. Normally, the aquarium heater is hung over the side ofthe tank by means of a housing, and the heating element is containedwithin a tube depending from the housing. Inside the tube is alsocontained an appropriate thermostat which senses the temperature.Typically, a bimetallic thermostatic switch is utilized, having a fixedand adjustable control member. The two control members are initiallyplaced in appropriate contact position in accordance with the desiredtemperature level. As the surrounding temperature of the water changes,the bimetallic control members will move into and out of engagement witheach other in order to open and close the circuit.

The heater is normally placed in the circuit and is turned on and off bymeans of the bimetallic switch. Usually, the heater is placed at thelower end of the tube and the bimetallic elements and other circuitmembers are contained in the upper part of the tube. The control of thetemperature level is generally obtained by means of a control knobplaced on the housing with indicia on the knob so that the desiredtemperature level can be selected externally of the aquarium tank.

In order to prevent arcing or pitting of the contacts, a capacitor istypically placed in parallel across the contact switch. Additionally, anindicator bulb, or the like, is generally included in parallel with theheating element to provide an indication when the heating element isturned on. Numerous heaters are described in the prior art. Typically,an aquarium heater is described in U.S. Pat. No. 3,731,058 which showsan aquarium heater of the type described and includes a unique heatingcoil arrangement which maintains uniform heating. Another prior artaquarium heater is described in U.S. Pat. No. 3,107,289 which againutilizes a basic structure similar to that described, and furtherincludes two bimetallic switches in parallel in order to preventfreezing or sticking of the contact members of the first one of theseswitches.

While these and other aquarium heaters are generally in use, one of theproblems with such heaters concerns the maintenance of the temperaturelevel as close as possible to the desired value. The thermostat withinthe tube should monitor the temperature of the aquarium water and reactto that temperature alone. However, since it is positioned in the tubeadjacent to the heating element itself, it is also affected by suchheating element. As a result, the heat reflected from the heatingelement is sensed by the thermostatic switch so that the switch mayreact to this increase in temperature and turn off the heating element,although actually, it is not the aquarium water that has risen intemperature, but it is only the effect from the heating element whichhas raised the temperature at the thermostatic switch. Therefore, inprior art heaters, there is more frequent turning on and off of theheater, and more difficulty in maintaining the temperature level of theaquarium water at the desired value. Additionally, the continued turningon and off of the bimetallic switch more than necessary, can causepremature carbonization and/or pitting of the switch contacts.

Additional problems with prior art devices concern the propermanufacture and maintenance of the device. Generally, the housing isformed of molded plastic which is manufactured to particular tolerances.The tube, typically of glass, is manufactured seperately and also hasits own broad tolerances. As a result, the spacing between the tube andthe housing can vary between different aquarium heaters. With prior artdevices, little, if anything, is done to accommodate such variations andaccordingly problems of excessive heat leakage, water seepage fromaeration bubbles, poor efficiency, and difficulty in maintenance isoften encountered because of such variations.

A further problem of prior art devices concerns the specificconstruction whereby the control chassis supporting the thermostaticelements is frequently utilized to lock the housing onto the tube. Forexample, in U.S. Pat. No. 3,107,289, there are locking members on thecontrol chassis which extend upwardly into the housing and are utilizedfor locking the various parts of the housing onto the tube. As a result,should movement of the tube occur, as for example during shipping and/oractual use, the control chassis together with the thermostatic elementswill be jarred and invariably moved from their preset position.Likewise, various electrical leads, capacitor, indicator bulb, and othercircuit components can also be displaced as the housing portion and thetube are slightly moved relative to each other. Such displacement canfrequently occur during actual utilization of the aquarium heater as itis being installed on the aquarium tank. During such installation,manipulation of the housing with relation to the tube always occurs.With prior art devices, such manipulation will effect the controlchassis and accordingly the thermostatic elements, which can permanentlydamage the aquarium heater. Also, even if it does not damage the heater,it may modify the present positioning of the contact members forming thethermostatic switch, whereby the initial setting on the control knobwill no longer be accurate to the desired temperature setting and notinfrequently can harm the fish by too great a temperature deviation.

Yet other problems with prior art devices concern the method andapparatus utilized for controlling the setting of the temperature levelat the desired value. The most common device utilized for such controlis a screw. For example, in the aforementioned patent, there is utilizedan adjustable screw rotated by a control knob which bears against abridge arrangement interconnecting the adjustable contact with respectto the fixed contact. Such screw arrangement can fail during continuedutilization, where the screw or opposing threads can become stripped.Also, the screw can lock the bridge arrangement into place whereby itcannot be raised, and the temperature level may be thereby held at acritically dangerous high level. The threaded metal or plastic rodutilized as the screw in prior art aquarium heaters is not perfectlystraight and therefore wobbles or turns eccentrically, creating anon-linear temperature range. Therefore, when the screw is turned toraise or lower the temperature slightly, the wobble acts in reverse. Thescrew arrangement has been a difficult one to maintain as well asutilize in order to provide accurate and efficient temperature setting.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide anaquarium heater which avoids the aforementioned problems of the priorart devices.

A further object of the present invention is to provide an aquariumheater which includes a housing with a depending tube, a thermostaticcircuit and a heating element being contained within the tube, wherebythe thermostatic circuit is sufficiently separated from the heatingelement so as to minimize any effect thereby.

Still a further object of the present invention is to provide anaquarium heater having a housing with a tube depending therefrom,wherein the tube contains a control chassis supporting thermostaticelements wherein the control chassis securely retains the thermostaticelements in place so that they cannot be jarred or moved from theirposition.

A further object of the present invention is to provide an aquariumheater having a housing with a depending tube, containing a thermostaticcontrol chassis and heating element, and wherein the housing and thetube are coupled together independently of the control chassis.

Still a further object of the present invention is to provide anaquarium heater having a housing and a depending tube, with athermostatic control chassis contained in the tube, and with avertically slidable actuating arm engaging a bimetallic thermostaticelement on the control chassis, to thereby adjust the desiredtemperature setting.

Yet another object of the present invention is to provide an aquariumheater having a housing and a depending tube, the tube containing athermostatic control chassis and a heating element, and having acircular cam surface on the housing engaging a vertical slidableactuating arm on the control chassis, for adjusting the desiredtemperature setting of the heater.

Still a further object of the present invention is to provide anaquarium heater having a housing with a tube depending therefrom, andwhich includes clamping members to accommodate variations in the size ofthe tube and its lip as well as the manufacturing tolerances of thehousing.

Yet a further object of the present invention is to provide an aquariumheater having a housing and a tube depending therefrom, with a controlchassis in the tube wherein the control chassis is formed as twosections matingly engaged in nesting relationship to form a cylindricalunit snugly fitting within the tube and securely holding thermostaticcontrol circuit elements therein.

The above objects are effected in accordance with the present inventionby providing an aquarium heater having a housing and a tube dependingtherefrom. An electrical heating element and a thermostatic controlchassis are disposed within the tube. The tube has a closed bottom andan open mouth surrounded by an outwardly extending peripheral lip. Thehousing includes a base portion and a cover portion in matingrelationship. The base portion has a bottom wall and a perimetricupstanding side wall surrounding the bottom wall. The bottom wallincludes an aperture through which the tube extends. A gasket surroundsthe tube and is interposed between the peripheral lip and the bottomwall. A locking ring fits within the upstanding side wall and clamps thelip of the tube against the gasket whereby the tube is retained in thehousing independently of the control chassis.

One type of locking ring that is described includes a keyway whichreceives a corresponding key located on the perimetric side wall of thebase portion. A tapered facing relationship exists between the key andthe surface of the locking ring to provide a wedging actiontherebetween.

In the present invention, the heating element is disposed at the bottomportion of the tube and the thermostatic control chassis is disposed inthe upper portion of the tube. The control chassis comprises twoopposing sections matingly engaged in nesting relationship to form acylindrical unit which snugly fits within the tube. The cylindrical unitincludes a base wall transversely separating the bottom portion of thetube from the rest of the control chassis. Bimetallic thermostaticswitch means are securely mounted within the cylindrical unit in circuitwith the heating element. Other circuit elements are likewise retainedsecurely in the control chassis in fixed position. An adjustment meanson the housing is provided for adjusting the position of the switchmeans to thereby control the temperature setting of the heater.

The adjustment means includes an actuator arm vertically slidable withinthe control chassis and extending upwardly into the housing. A controlknob having a cam surface thereunder is provided for convertingrotational movement of the control knob into vertical sliding movementof the actuator arm. The actuator arm bears against an adjustablecontact member of the bimetallic switch means and adjusts the relativeposition of the contact members for the desired temperature value.

BRIEF DESCRIPTION OF THE DRAWINGS

With the above and additional objects and advantages in view, as willhereinafter appear, this invention comprises the devices, combinations,and arrangements of parts hereinafter described and illustrated in theaccompanying drawings of a preferred embodiment in which:

FIG. 1 is an exploded view of the aquarium heater in accordance with thepresent invention;

FIG. 2 is a partially cut away front elevational view;

FIG. 3 is a sectional view taken along line 3--3 of FIG. 2;

FIG. 4 is an exploded view of the parts of the base portion of thehousing;

FIG. 5 is a sectional view taken along line 5--5 of FIG. 2, and showingthe bimetallic switch in a first position;

FIG. 6 is a fragmented view similar to that of FIG. 5, showing thebimetallic switch in a second position; and

FIG. 7 is a schematic circuit drawing of the electrical system of theaquarium heater.

In the various figures of the drawing, like reference charactersdesignate like parts.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings, and particularly to FIGS. 1, 2 and 5, theaquarium heater is shown to include a housing, shown generally at 10,and comprising a base portion, shown generally at 12, and a coverportion, shown generally at 14, including a cap member 16. Downwardlydepending from the housing 10 is a tube, shown generally at 18, having acylindrical configuration with a closed U-shaped bottom 20 and an opentop. An outwardly directed peripheral lip 22 surrounds the open top.Disposed within the tube, and particularly in the lower portion thereof,is a heating element 24 electrically connected to a thermostatic controlchassis, shown generally at 26, positioned in the upper portion of thetube.

The base portion 12 of the housing can best be seen with reference toFIGS. 1, 4 and 5. Such base portion 12 includes a bottom wall 28 havinga circular section 30 with a laterally extending section 32. On thecircular section 30 of the bottom wall 28 is a perimetric upstandingside wall 34 surrounding an aperture 36 provided in the bottom wall fromwhich depends the tube 18. An upstanding perimetric outer side wall 38is spaced from and surrounds the perimetric side wall 34. The twoperimetric walls 34, 38 and the portion of the bottom wall 28 betweenthe two perimetric walls provides a moat section or recess 40 which canreceive leakage water, as will be described hereinafter. The perimetricside wall 34 terminates in a plane slightly above the perimetric outerside wall 38. The outer side wall 38 is formed proximate the outer edgeof the circular section 30 and the opposite side edges of the section 32of the bottom wall 28.

Provided on the laterally extending section 32 of the bottom wall 28 areupstanding separating walls 42 defining passageways 44 therebetween,through which lead wires may extend. Notches 46 are provided at theupper edge of the perimetric side wall 34 to receive the lead wiresextending upwardly from the control chassis contained within the tube18. Two such notches 46 are provided corresponding to the two leadwires. These wires then pass through the passageways 44 and arepositioned together for passage through a single notch 48 provided in arear flange 50 on section 32. The flange 50 is positioned perpendicularto the bottom wall 28 and against the opposite ends of the side wall 38.The flange 50 in conjunction with a depending L-shaped member 52provides the clamping mechanism for securing the aquarium heater to aside wall of the aquarium tank. An aperture 54 is provided in the flange50 to accommodate a locking screw (not shown) for retaining the aquariumheater in place on the aquarium tank wall.

The cover portion 14 includes a top wall 56 which is correspondinglyshaped to fit over the bottom wall 28 of the base portion 12 of thehousing. Downwardly depending side walls 58 extend from the top wall andare formed with a stepped section 60. The stepped section 60 fits overthe upper edge of the outer perimetric side wall 38 and sits upon it. Adownwardly depending internal post 62 is integrally formed with the topwall 56. The post 62 sits on the laterally extending portion 32 of thebottom wall 28 of the base portion, and receives therein a clampingscrew 64 for securely retaining the cover portion onto the base portionand completing the housing. A rear portion 66 of the cover member 14 ispositioned to lie on the upper edge of the flange 50 to define a rearwall. The lead wire 68 passes under the rear portion 66 and in the notch48 provided in the flange 50 of the rear wall, as shown in FIG. 3.

An aperture 70 is provided in the top wall 56 of the cover portion andreceives therein the cap member 16. The cap member includes a circularknob 72 having knurled or spleened periphery side walls 74 to permitgrasping for rotation of the knob. Graduations can be formed on theknob, and an index marker can be formed on the cover portion, whichtogether can be calibrated to read appropriate temperature levelsettings.

The downwardly depending side walls 74 of the knob terminate in anoutwardly extending flanged portion 76 which in turn terminates with adownwardly depending rim 78. The outwardly extending flanged portion 76sits on the upper edge of the perimetric side wall 34 and is maintainedsituated below the top wall 56 of the cover portion by means of theupwardly extending retaining wall 80 of the flanged portion 76. A step82 is provided in the top wall 56 for seating and holding the retainingwall 80.

With the position as shown, the downwardly depending rim 78 extends intothe moat section 40. This provides a safety feature for the apparatus.Under normal operation, only the downwardly depending tube 18 ispositioned within the aquarium water. The housing 10 is normallymaintained above the water level. However, it may accidentally occurthat the housing itself may become splashed or water may be accidentlypoured over it. Any water which seeps into the housing, and specificallyfrom around the rotating cap member 16, will be directed by means of theoutwardly extending flange 76 and the downwardly depending rim 78 intothe moat section 40 where the water will drain off through hole 41 inthe bottom wall 28, best shown in FIG. 3. This will prevent waterseepage into the tube 18 where it might damage the electrical componentsand possibly cause electrical failure of the device.

The downwardly depending tube 18 is clamped to the housing by means of aclamping mechanism best seen in FIGS. 4 and 5. At least two inwardlyprojecting keys 84 are provided spaced around the inside surface of theperimetric side wall 34. The lower surface 86 of each key is downwardlytapered. A circular washer, O-ring or gasket 88 is provided forpositioning beneath the lip of the tube 18, and a clamping or lockingring 90 is utilized for clamping the tube to the housing. The lockingring includes keyways 92, 94 in the outer periphery thereof and circularrelief grooves 96 provided in the upper surface.

In assembly, as can best be seen in FIG. 5, the washer or gasket 88 isplaced around the periphery of the tube and abuts the underside of theoutwardly extending tube lip 22. The tube is then inserted in theaperture 36 in the bottom wall 28 at the circular section 30 of the baseportion 12 so that the gasket lies on this bottom wall. The locking ring90 is then inserted into the aperture 36 so that the keyways 92, 94receive and bypass the keys 84, and the locking ring is then turned.Because of the tapered lower surfaces 86 of the keys, as the lockingring is turned under the keys 84, a wedging action takes place along theupper surfaces of the locking ring whereby it tightly clamps the lip ofthe tube against the gasket and retains it within the base portion.

Although the above wedging action was shown as having the lower surfaceof the keys tapered, it is understood that alternatively the uppersurface of the locking ring could be likewise tapered with the lowersurface of the keys not being tapered. Additionally, in place of the keyand keyway arrangement, the locking ring could be screwed into place byhaving an internally threaded surface provided in the perimetricsidewall 34, and having an externally threaded perimeter provided aboutthe locking ring.

By means of the clamping arrangement described above, it will beappreciated that the tube depends from the housing and is clamped to thehousing without any association with or without the assistance of thethermostatic control chassis. Accordingly, should there be any relativemovement between the tube and the housing, it will not cause thethermostatic elements to become dislodged, jarred, or displaced fromtheir independent position within the tube. Additionally, by means ofthe gasket arrangement, numerous variations in size, resulting fromtolerance limitations, can be accommodated. Thus, any variations in sizein the tube itself, particularly the lip size, will be compensated bymeans of the gasket whereby a tight fit will still be provided betweenthe housing and the tube to support the tube and to prevent seepage ofwater therein.

It should be appreciated, in this regard, that normally the gasket wouldbe assumed to be placed beneath the locking member 90 so that thelocking member clamps against the gasket. However, by placing it on theunderside of the lip, and specifically between the lip and the bottomwall 28 of the base portion 12, a supporting seal is provided betweenthe lip and the bottom wall which compensates for any variation that mayoccur during manufacture, particularly the manufacture of the tubewithin given tolerance limits. Aeration of the water in the aquariumgives rise to bubbles popping at the surface which would wet andinfiltrate through this point so that the seal serves a dual purpose.

The control chassis 26 is formed of opposing housing sections 100 and102. Each housing section is of a semicylindrical shape comprisingrespective outer walls 104, 106, respective semicircular bottom walls108, 110, and respective upper flange section 112, 114, and 116, 118.

The two housing sections matingly engage with each other in nestingrelationship to form a composite cylindrical housing unit whose outerwall snugly fits within the tube 18. As will hereinafter be explained,the various thermostatic circuit elements are all maintained with thiscylindrical housing unit in fixed relationship therein. Because of thissnug fit, there will be avoided the jarring of the various thermostaticcircuit elements within the tube, and once preset, these circuitelements will be maintained in appropriate desired position.

The two semicircular bottom sections 108, 110, also interfit to form atotal bottom wall which separates the heating element 24 from thethermostatic circuit elements as shown in FIG. 5. In this way thethermostatic circuit elements, and particularly the bimetallic switch,will insufficiently be affected by the heating in the bottom portion ofthe tube and will only be affected by the temperature of the surroundingwater.

Contained within the housing section 100 are inwardly directed,longitudinally extending spacer walls 120, 122, defining therebetween achannel portion 124. An opening 126 is formed in the outer wall 104 ofthis housing section commensurate with at least a portion of the channel124, as can best be seen in FIG. 2. Positioned along the channel is afirst mounting pad 128 which includes therein a rivet hole 130. Furthertherebeneath, is an additional mounting pad 132 also containing a rivethole 134.

On the side of each spacer wall 120, 122 are provided guideways forreceiving therein lead wires. Against the bottom wall 108 are providedthe guide posts 136, 138 defining the space 140 therebetween forreceiving the lead wire 142 as it passes beneath the bottom wall. On theother side of the spacer wall 122 are provided additional guide postsfor permitting passage of another lead wire on the other side thereof.An additional center guide post 144 is provided for defining guidewayson either side to receive the wires going to the bulb. Notches 146 areformed in opposite portions of the bottom wall to permit passagetherethrough of the lead wires. Corresponding notches 148 are alsoprovided on each of the top sections 112, 114 to permit entry of thelead wires therein. Appropriate recesses or slots 150, 152 are formed inthe spacer wall 122 to permit threading of the lead wires therethroughso as to bring the lead wires from the outer guideways into the channel124 for appropriate electrical connection to the bimetallic switchmembers.

In the other housing section 102 are also formed longitudinallyextending spacer walls 152, 154, defining therebetween the channel 156.An opening 158, shown in FIG. 5, is formed in the outer wall 106 of thishousing member permitting access to at least a greater portion of thechannel 156. A stepped mounting pad 160 is formed with correspondingapertures 162 and 164 formed on each step.

The two channels 124, 156 respectively formed within the two housingsections 100, 102 are opposing each other and are so formed that thespacer walls respectively defining these channels will also form anabutting relationship with each other. Accordingly, the spacer walls120, 122 extend past the semicircular outer wall 104 of the housingsection 100 so that they can mate with the recessed spacer walls 152,154 in the section 102. The two channels will thereby be incommunication with each other.

In the housing section 104, it will be noted that at the lower portionthereof there is formed an L-shaped baffle wall including the upper wallsection 166 and the side wall section 168. The side wall section 168lies along the same plane and is commensurate with the spacer wall 120thereabove. The spacer wall 122 continues downwardly to form a side of ahousing defined by the baffle walls 166, 168, the lower part of thespacer wall 122 and the bottom section 108. These four walls form aninternal chamber 184 for receiving therein an illuminating bulb 170. Anaperture 172 is formed in the outer wall 104 of the housing section 100,as shown in FIG. 5, to permit viewing of the illuminating bulb. A bezel174 can be placed in the aperture 172 and a diffusing plate 176, such asa piece of translucent glass or plastic, can be placed within the bezel,as shown in FIGS. 2 and 5.

A resistor 178 is placed in series with the illuminating bulb 170 andthe two lead wires 180, 182 extending therefrom. The wires 180, 182downwardly depend from the internal chamber 184. These wires 180, 182pass through the guideway formed between the posts 138 and 144 on theone side, as well as the guideway formed on the other side of the post144.

A transverse baffle plate 188 is formed in the housing section 102 witha notch 186 in the front face thereof. The plate 188 is opposed to thechamber 184 so that the notch 186 can serve to support the indicatorbulb 170 and maintain it in place.

The bimetallic switch is formed of a fixed contact member 190 and acorresponding adjustable contact member 192. Each contact memberincludes the respective contact points 194, 196 which are spaced toengage each other when contact is made. The fixed contact member 190 hasan aperture 198 at its lower end and is positioned on the outward sideof the mounting block 128. It is spaced within the channel 124 providedbetween the spacer walls 120, 122. Because of the aperture 126 formed inthe outer wall 104 adjacent this channel, the fixed contact member canbe affected by the temperature of the surrounding water.

Rivet 200 is utilized for the purpose of connecting the fixed contactmember 190 within its channel. At the same time, the rivet 200 alsointerconnects the terminal lug 202 of the lead wire 204. It also servesto contact the loop terminal 206 of the capacitor 208 and makeelectrical contact therewith.

Initially, the lead wire 204 passes downward into the control chassisthrough the notch 148 in the top flange 114, then along the guidewayprovided on the lateral side of the spacer wall 122, and is then bentinwardly through the space 152 to be in position for mounting onto themounting pad 128. The capacitor is maintained in the space between themounting pads 128 and 132 on the one hand, and between the two spacerwalls 120, 122 on the other hand.

The adjustable contact member 192 is maintained within the channel 156in the other housing section. Its lower end has a vertical section 210having two apertures 212 and 214 which align with the apertures 162, 164of the mounting pad 160. The adjustable contact member 192 is connectedon the outer side of the mounting pad, and fits within the channel, asshown in FIGS. 5 and 6. The aperture 158 provided in the outer wall 106which gives access to the channel 156 also permits the adjustablecontact member to be affected by the temperature of the aquarium water.

A first rivet 216 is utilized in conjunction with the lower aperture 164and simultaneously serves to clamp the other looped contact 218 of thecapacitor as well as the terminal lug 220 of the lead wire 222. Afurther rivet 224 (FIG. 5) is utilized for passing through the aperture134 in the mounting block 132 and into the aperture 162 in the mountingblock 160 for securely holding together the two opposing sections of thehousing. The lead wire 222 passes through the space 150 and thendownwardly through the guideway provided between the wall 122 andguidepost 226, downward through the notch 146 and the adjacentguideposts and then below the control chassis.

The lead wires 222 and 142 downwardly depending from the bottom wall ofthe control chassis, together with the lead wires 180 and 182 from theilluminating means, are connected in parallel and are placed within theterminal jacks 228, 230. The terminal jacks pass downwardly and areinserted into the sockets 232, 234 which are connected to the core 236of the heating element 24. A resistance heating wire 238 is coiledaround the core to form the appropriate heating element, as is wellknown in the art.

The electrical circuit showing the connections heretofore described isschematically shown in FIG. 7. It will be appreciated that thebimetallic contact switch having the members 190, 192 has placed acrossit the capacitor 208 for preventing arcing and accordingly avoidingpitting of the contact points on the contact members. This combinationis placed in series with the heater coil 24. Placed in parallel acrossthe heater coil is the series combination of the illuminating bulb 170and the resistor 178.

Adjustment of the temperature setting is achieved by means of a uniquesliding arrangement shown best in FIGS. 5 and 6. Formed in the upperpart of the channel 156 of the housing section 102 is a passageway. Thecross bars 240 and the cross plate 242 define the front portion of thispassageway. Within the passageway there is provided the slidingactuating arm 244 having an upper curved cam follower surface 246, asshown in FIG. 1.

The cam surface which operates the actuating arm 244 is formed on theunderside of the cap 16. Specifically, it comprises the flat circularsurface 247 which is angularly positioned on the underside of the cap16. This is achieved by means of the depending walls 248 and 250 withone of the walls 248 being longer and lower than the other wall. As aresult, the flat surface 247 is positioned with one end disposed lowerthan its diametrically opposed other end. The cam surface 247 serves toconvert rotating motion of the cap into longitudinal motion for movementof the actuating arm 244.

The adjustable contact member 192 is formed with a plurality ofsections, including the first angular section 251 upwardly extendingfrom the vertical mounting section 210. There is then provided thelongitudinal section 252 followed by a V-shaped section having a lowerarm portion 254 continuing with the upper arm portion 256 andterminating with the upward longitudinal section 258. The contact point196 is formed on the uppermost section 258. The shape of the adjustablecontact member is such as to provide a leaf spring action which biasesthe sliding member 244 into an upward position.

The operation of the adjusting means can best be explained withrelationship to FIGS. 5 and 6. In FIG. 5 it will be noted that the camsurface 247 is adjusted so that its dwell, or lowermost portion isagainst the cam follower edge 246 of the actuating arm 244. Accordingly,the forward arm portion 256 of the V-shaped section of the adjustablecontact member 192 biases the actuating arm 244 into its uppermostposition, whereby the adjustable contact member is at its rightmostposition, with its contact point 196 being spaced apart from the contactpoint 194 on the fixed contact member 190.

As the knob 16 is rotated, the cam surface 247 rotates such that a lowerpart of the cam moves into contact with the cam follower 246 and lowersthe actuating arm 244 to its lowermost position, as shown in FIG. 6. Thelower end of the actuating arm 244 bears against the arm portion 256 ofthe V-shaped section of the adjustable contact member 192 so as to pushit into a downward position as shown in FIG. 6. With the movement of thearm portion 156 downward, the upper section 258 moves to the lefttowards the contact point 194 and into engagement with it, and continuesto move along and push the contact point 194 until the fixed contact 190is in a slightly bent position, as shown in FIG. 6.

Depending upon the initial positioning between the adjustable and fixedcontact members, the appropriate temperature setting will be achieved.The further the contact members are moved to the left, as shown in FIG.6, the higher the temperature required to open the contacts and shut offthe heating element of the heater. The less initial contact between themembers, as in FIG. 5, the smaller the temperature needed to separatethe contacts and shut off the heating element of the heater.Accordingly, by rotating the upper knob, the proper contact can beachieved and the proper temperature setting adjusted to maintain thetemperature level of the heater as close as possible to a desired value.

It will be appreciated that by means of the knob and sliding actuatingarm arrangement, a cyclical control is achieved so that after a crest inthe cam is achieved, it begins to approach a dwell portion, and thencontinues again towards a crest. As a result, if the cam gets stuck inone of its maximum positions, only a slight movement will move it offthe maximum onto a lesser position. This then provides a safety featureto avoid problems in the adjustment. Furthermore, the arrangement bymeans of a sliding arm avoids the need of a screw which has a tendencyof wearing down, getting stuck, and providing difficulty in utilization.

The upper edge of the control chassis extends above the open end of thetube and extends transversely outwardly therefrom. This end extends intothe housing and is held in place by means of a step portion internallyformed on the upstanding side wall 34 which forms a seat receiving thetop wall of the chassis. A downwardly depending rib 260, as shown inFIG. 6, extending below the outer flange 76 of the cap, maintains thecontrol chassis in its downward position. At the same time, this annularrib permits rotation of the cap thereon.

It is appreciated that by means of the control chassis all of thecontrol elements of the thermostatic circuit are maintained securely inplace and will not move about or become jarred during operation.

Numerous alterations of the structure herein disclosed will suggestthemselves to those skilled in the art. However, it is to be understoodthat the present disclosure relates to a preferred embodiment of theinvention which is for purposes of illustration only and is not to beconstrued as a limitation of the invention.

What is claimed is:
 1. An aquarium heater comprising a housing and atube depending therefrom, an electrical heating element and athermostatic control chassis disposed within said tube, the controlchassis comprising a bimetallic thermostatic switch comprising a fixedcontact member and an adjustable contact member, and adjustment meansfor adjusting the relative positions of said contact members to therebycontrol the temperature setting of the heater, said adjustment meanscomprising an actuator arm vertically slidable within said tube toengage said adjustable contact member and laterally adjust its position,and control means in said housing for controlling the vertical positionof said actuator arm in accordance with the desired temperature setting,said control means comprising a rotatable control knob, and means forchanging rotary motion of the control knob into vertical motion of theactuator arm.
 2. An aquarium heater as in claim 1, wherein said changingmeans comprises a flat circular surface positioned beneath said controlknob with one edge lower than its diametrically opposed edge to therebyprovide a cam surface, an upper end of said actuator arm engaging saidcam surface.
 3. An aquarium heater as in claim 2, and further comprisingmeans for biasing said actuator arm in an upward direction.
 4. Anaquarium heater as in claim 2, wherein said adjustable contact membercomprises an elongated strip having a V-shaped section laterallyprovided along its length, and wherein said actuator arm bears againstan upper portion of said V-shaped section.
 5. An aquarium heater as inclaim 1, and further comprising a passageway provided in said controlchassis for slidably receiving said actuator arm and permitting saidactuator arm to extend above said control chassis and into the housingfor engagement with said control means.